It wasn't that long ago that medicine declared a victory over infectious disease. Now a raft of new and mutating bugs are at the door, and a declining public health system is in no shape to fight them.

As with AIDS, it took years for TB to be recognized as a serious problem. Today, both are seen as "urban diseases," disproportionately afflicting the poor and people of color. In addition to homeless shelters, prisons and dormitories provide ideal conditions for TB's spread. By 1991, almost $700 million was spent nationwide on an epidemic centered on the East Coast, but reaching all the way across the continent. Minnesota officials report about 140 new TB cases each year.

TB, though potentially lethal, is entirely treatable with antibiotics. Thus, for a long time docs simply gave their patients bottles of pills and told them to take this twice a day, this three times, and come back every other day for a shot. Many patients--illiterate, too poor to afford bus fare, or simply too busy surviving--didn't complete treatment, got sick again, and went on to infect more people.

And along the way something else happened. After being exposed to antibiotics for a while, the TB bacteria began to mutate; strains that could elude the chemicals had a better chance of survival. If treatment was completed, the bugs not killed by one antibiotic would usually succumb to another. But if patients didn't take all the meds, resistant strains multiplied. The next infection was that much harder to treat. After a while, bacteria emerged that could resist several classes of antibiotics. By 1992, around 8 percent of new TB cases around the country were multiple-drug resistant, as were almost one in four relapsing cases. So far, no TB strains have been seen that resist all known drugs, but many researchers say the clock is ticking.

In the decades since World War II, doctors have been throwing antibiotics at everything but the kitchen sink. Patients who asked could get them for a cold; some people were given the meds simply as a preventive measure. The drugs were also routinely dumped into animals and animal feeds. Even vegetables grown in manure-fertilized fields have been found to contain antibiotics, and bugs resistant to them.

A predictable vicious cycle has ensued. The remaining effective antibiotics are now often prescribed in higher doses and wider combinations, giving bacteria yet more incentive to mutate. Evidence has emerged that bacteria can "learn" from each other, passing pieces of genetic code even across species. And once germs become resistant, even seemingly innocuous infections can turn catastrophic: Older people still remember the days when you needed to carefully watch a cut because if it turned red and swelled, you might have a wound infection that could result in amputation and death.

Ironically, the ultimate bacterial resistance labs are health care settings, especially hospitals, where bugs find a variety of hosts with weakened defenses. The most vulnerable are AIDS, cancer, and transplant patients who are given powerful drugs to suppress their immune systems. They might pick up dozens of infections at one time and then take multiple powerful antibiotics, making them what one researcher calls "human petri dishes."

In 1992, 90 percent of staphylococcus aureus, the bacteria involved in toxic shock syndrome that can also kill surgery patients, were found resistant to penicillin and other antibiotics. Staph infections are common in hospitals, and only one type of antibiotic--vancomycin--reliably works against them any more. But another class of bug, enterococci, are already resistant to that one, and they commonly coexist with staph in the same patient. Earlier this year, scientists for the first time showed vancomycin resistance passed between the bugs in the test tube; it may be only a matter of time for the same thing to happen in humans.

At Hennepin County, says infection-control coordinator Dr. Margaret Simpson, "we've so far been lucky" not to see vancomycin-resistant enterococci. The hospital does have staph aureus infections, and about 10 percent of them are multiple-drug resistant; Simpson says at some metro-area hospitals the rates are much higher. All area hospitals have had to come up with new infection-control measures; some patients with highly contagious infections are put in "respiratory isolation" rooms which don't vent to the rest of the hospital, and where caregivers go with specially fitted "Darth-Vader-type" masks. "We go through waves of fear occasionally," Simpson says, "when we realize that this is becoming a reality. When I was trained, most of these diseases were nonexistent or could be treated. People of my generation now have had to work through that and decide if they want to continue being a health care worker."

Bacteria aren't the only bugs developing resistance to what were once thought the ultimate weapons against them. HIV can mutate so fast that a patient's infection will split off resistant strains almost as soon as an antiviral medication is given. Tiny parasites that live in drinking water have learned to evade chlorination. Even bugs in the literal sense can develop resistance; there are strains of mosquitoes that are unbothered by various pesticides.

New discoveries are unlikely to come to the rescue. After 50 years of mining evolution for the chemicals microbes deploy against each other, science has found all the easy ones, and researchers say new antimicrobial drugs will be few and far between. Last year, only two were approved by the FDA; both targeted HIV. "There's nothing on the shelf," one bacteriologist told reporters last year, talking about resistant staphylococcus. "Nothing on the pipeline. If we lose vancomycin, we're going to be back to the 1930s."